Nowadays, technology is very advanced. Internet plays an important role in everyday life. And it is indispensable. It is as important as the electrical system. And because HappyPOS is a mobile-based system and work simultaneously. It can not be used offline, but can use in case of Internet stumble or jam in a short time. And HappyPOS can use the backup system of the main Internet system off-line. For example, in conjunction with mobile phone SIM card, etc. And in case of power outages, HappyPOS will continue to operate on the Internet by using on mobile devices as well.